Telescopic power transmission units are frequently used in off-road vehicles, such as tractors, logging equipment, heavy construction equipment, and the like. U.S. Pat. No. 3,293,884 describes a power transmitting unit composed of a pair of telescopic, tubular, splined or axially grooved members. The spline sections permit relative axial or telescopic movement between the members and yet provide a positive torque transmitting connection.
The use of hollow members or tubes in a power transmitting unit has distinct advantages in the design of a vehicle propeller shaft over the use of bar stock which is machined to provide the spline connection. Torque is best transmitted by tubular members, for under heavy reverse torque load and side load, the relatively large diameter tubular members will more effectively resist stress and increase the duration of use before failure. Furthermore, due to the inherent elasticity of the tubular member, the splined teeth can retreat or push out under torque load so that all of the spline teeth will be in engagement and take the load regardless of any possible inaccuracy in the formation of the teeth.